Upon Caloric as a Cause of Galvanic Currents. 275 



are capable of generating, when placed in contact ^remows to the ap- 

 plication of heat. In general, very small fragments or wires, and the 

 flame of a spirit lamp, will furnish satisfactory results ; but, in some 

 instances, one of the metals must be employed in large masses and 

 the requisite temperature obtained by a charcoal fire. 



The disturbance of the ordinary currents, is momentary, or at 

 least, lasts only while the difference of temperature continues so 

 great as to give the caloric a direction contrary to that which it would 

 take when the metals are heated in contact with each other. 



A few examples will render the nature of these modifications more 

 apparent. 



Antimony, when heated in contact with the following metals, bis- 

 muth, nickel, copper, platinum, &.c. invariably conveys a positive 

 current to the galvanometer; but when made obscurely red-hot, 

 previous to the contact, its polarity becomes reversed with every 

 metal tried, except bismuth, nickel and mercury, which, being at 

 the remote end of the thermo-electric scale, in relation to antimony, 

 exhibit only a feeble diminution of force. The conclusion obvious- 

 ly to be drawn from this example, is, that antimony, while in contact 

 with copper, platinum and most other metals, receives caloric from 

 them ; because, when, by excess of heat, it is compelled to give it 

 out, the ordinary galvanic currents become reversed. Another re- 

 sult is, that in such cases the caloric and positive current move in the 

 same direction. Upon referring to the electrical condition of hs par- 

 ticles, when unequally heated, as before stated, it will be seen that an 

 increase of heat makes antimony transmit a positive current, so that 

 it is obvious, this metal governs the currents proceeding from the 

 combinations just noticed, according to its own elementary condition 

 in relation to caloric. 



Bismuth furnishes examples of the opposite character. Its po- 

 larity continues uniform, whether it is heated in contact with the met- 

 als, or whether the latter are made hotter or colder, previous to the 

 contact. But, in most cases, its power of transmitting a negative 

 current is diminished when the caloric is made to proceed from it, 

 and, as this diminution is undoubtedly indicative of a tendency to- 

 wards inverted polarity, we may infer that in all its thermo-electric 

 combinations, it acts by receiving caloric, like antimony — such a con- 

 clusion is strengthened by the elementary condition of its own par- 

 ticles, which, it has been shown, become capable of transmitting a 



